The invention relates to a device for recirculating and cooling exhaust gas of an internal combustion engine according to the preamble of claim 1 and also to an arrangement for recirculating and cooling exhaust gas according to the preamble of claim 10, which are each known through U.S. Pat. No. 6,244,256 B1.
Exhaust-gas recirculation (abbreviation: AGR), especially cooled exhaust-gas recirculation, is used in today's vehicles due to legal regulations, in order to reduce particulate and pollutant emissions, especially nitrous oxide emissions. Because requirements on exhaust-gas cleaning are becoming stricter, greater exhaust gas mass flows are necessary, which can be handled only conditionally with known AGR systems.
Known AGR systems are arranged on the high-pressure side of the internal combustion engine, as described in U.S. Pat. No. 6,244,256 B1 named above. The known AGR system has an exhaust-gas turbocharger for a diesel engine and an AGR line with an AGR valve, which is arranged between the engine and exhaust-gas turbine. The recirculated exhaust gas is cooled, preferably in two stages, i.e., in two exhaust-gas heat exchangers, which are each cooled by a separate coolant circuit and are constructed as high-temperature and low-temperature exhaust-gas coolers. The cooled, recirculated exhaust gas is combined with compressed and cooled charge air and fed to the intake tract of the engine.
Exhaust-gas heat exchangers, especially exhaust-gas coolers, are known in various embodiments: through DE 199 07 163 A1 of the applicant, a welded construction for an exhaust-gas heat exchanger became known, which is made from a bundle of exhaust-gas pipes, around which coolant flows on their outside. This coolant is removed from the cooling circuit of the internal combustion engine.
In many cases, exhaust-gas heat exchangers are also equipped with a bypass channel for the exhaust gas, i.e., for the case that cooling of the exhaust gas or, for heating purposes, heating of the coolant is not necessary or not advantageous. In DE 199 62 863 A1 of the applicant and in DE 102 03 003 A1, such exhaust-gas heat exchangers are disclosed with an integrated bypass, wherein in an inlet diffuser or in the outlet region of the exhaust-gas heat exchanger there is a bypass valve, preferably in the form of a bypass flap, which acts as a switch for the exhaust-gas flow and guides this flow either through the pipe bundle with coolant flowing around this bundle or through the bypass channel.
As is known by EP 1 030 050 A1, the bypass channel for the exhaust-gas heat exchanger can also be arranged separately, i.e., outside of the heat exchanger. In this known AGR system, the AGR valve is arranged, incidentally, in the return of the AGR line, i.e., behind the exhaust-gas cooler in the direction of the exhaust-gas flow.
Through DE 198 41 927 A1, a device for exhaust-gas recirculation became known with a valve device, in which a bypass channel with a bypass flap is integrated. The exhaust-gas heat exchanger has a bundle of U-shaped exhaust-gas pipes, which are cooled by a liquid coolant.
Through DE 197 50 588 A1, a device for exhaust-gas recirculation became known, in which an exhaust-gas heat exchanger with an exhaust-gas recirculation valve (AGR valve) is integrated to form a structural unit. Thus, a simplified and thus less expensive manufacture can be effected since individual parts can be eliminated.
A disadvantage in the known AGR systems is that these are made from a plurality of individual parts, which are produced separately and which are mounted individually, which increases costs. In addition, in the known AGR systems, it is disadvantageous that greater exhaust-gas flows cannot be recirculated since, due to the arrangement of the ASR system on the high-pressure side of the engine, the pressure difference between the exhaust gas side and the intake side of the engine are insufficient to discharge greater mass flows.